• Journal of computational fluids engineering
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• v.10 no.2
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• pp.48-53
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• 2005

This work discusses the numerical analysis, the design and experimental test of the SMA actuator along with its capabilities and limitations. Convective heating and cooling using water actuate the SMA(Shape memory alloy) element of the actuator. The fuel such as propane, having a high energy density, is used as the energy source for the SMA actuator in order to increase power and energy density of the system, and thus in order to obviate the need for electrical power supplies such as batteries. The system is composed of a pump, valves, bellows, a heater(burner), control unit and a displacement amplification device. The experimental test of the SMA actuator system results in 150 MPa stress(force : 1560 N) with $3\%$ strain and 0.5 Hz. actuation frequency. The actuation frequency is compared with the prediction obtained from numerical analysis. For the designed SMA actuator system, the results of numerical analysis were utilized in determining design parameters and operating conditions.

• Journal of the Korean Electrochemical Society
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• v.10 no.1
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• pp.7-13
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• 2007

We synthesized and investigated $La_{0.75}Sr_{0.25}FeO_3$ by Glycine Nitrate Process(GNP) method used as cathode materials for SOFC(solid oxide fuel cell). Optimized amount of glycine is 3.17 mol. ICP elemental composition analysis indicated that the stoichiometry of the synthesized powders have nearly nominal values. SEM images and XRD patterns reveal that the synthesized powder has uniform size distribution and high degree of crystallinity. The sample powders were isostatically pressed to form a pellet. The green body was sintered at $1200^{\circ}C$ and the relative density of the sintered specimens were measured by Archimedes mettled. We measured electrochemical performance of LSF by AC impedance spectroscopy. Resistance of LSF shows lower value than that of LSM throughout all temperature region. The anode-supported solid oxide fuel cell showed a performance of $342mW/cm^2(0.7V,\;488mA/cm^2)$ at $750^{\circ}C$. The electrochemical characteristics of the single cell were examined by at impedance method.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.16 no.2
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• pp.243-260
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• 2018

A literature review on the effects of high temperature and radiation on radiation shielding concrete in Spent Fuel Dry Storage is presented in this study with a focus on concrete degradation. The general threshold is $95^{\circ}C$ for preventing long-term degradation from high temperature, and it is suggested that the temperature gradient should be less than $60^{\circ}C$ to avoid crack generation in concrete structures. The amount of damage depends on the characteristics of the concrete mixture, and increases with the temperature and exposure time. The tensile strength of concrete is more susceptible than the compressive strength to degradation due to high temperature. Nuclear heating from radiation can be neglected under an incident energy flux density of $10^{10}MeV{\cdot}cm^{-2}{\cdot}s^{-1}$. Neutron radiation of >$10^{19}n{\cdot}cm^{-2}$ or an integrated dose of gamma radiation exceeding $10^{10}$ rads can cause a reduction in the compressive and tensile strengths and the elastic moduli. When concrete is highly irradiated, changes in the mechanical properties are primarily caused by variation in water content resulting from high temperature, volume expansion, and crack generation. It is necessary to fully utilize previous research for effective technology development and licensing of a Korean dry storage system. This study can serve as important baseline data for developing domestic technology with regard to concrete casks of an SF (Spent Fuel) dry storage system.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.13-16
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• 2008

Solid oxide fuel cell(SOFC) is an electrochemical energy conversion system with high efficiency and low-emission of pollution. In order to reduce the operating temperature of SOFC system under $800^{\circ}C$, the thickness reduction of YSZ electrolyte to be as thin as possible, e.g., less than 10 ${\mu}m$ are considered with the microstructure control and optimum design of unit cell. Methods for reducing the thickness of YSZ electrolyte have been investigated in coin cell. Moreover, a large unit cell($8cm{\times}8cm$) for SOFC was fabricated using an anode-supported electrolyte assembly with a thinner electrolyte layer, which was prepared by a tape casting method with a co-sintering technique. we studied the design factors such as active layer, electrolyte thickness, cathode composition, etc,. by the coin type of unit cell ahead of the fabrication process of a large unit cell and also reviewed about the evaluation technique of a large size unit cell such as interconnect design, sealing materials and current collector and so forth. Electrochemical evaluations of the unit cells, including measurements such as power density and impedance, were performed and analyzed. Maximum power density and polarization impedance of coin cell were 0.34W/$cm^2$ and $0.45{\Omega}cm^2$ at $800^{\circ}C$, respectively. However, Maxium power density of a large unit cell($5cm{\times}5cm$) decreased to 0.21W/$cm^2$ at $800^{\circ}C$ due to the increase of ohmic resistance. However, It was found that the potential value of a large unit cell loaded by 0.22A/$cm^2$ showed 0.76V at 100hrs without the degradation of unit cell.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.373-373
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• 2009

Relative humidity, membrane conductivity and water activity are critical parameters of polymer electrolyte membrane fuel cells (PEMFC) for high performance and reliability. These parameters are closely related with temperature. Moreover, the ideal values of these parameters are not always identical along the channels. Therefore, the cooling channel design and its operating condition should be well optimized along the all location of the channels. In the present study, we have performed a numerical investigation on the effects of cooling channels on performance of a PEMFC. Three-dimensional Navier-Stokes equations are solved with the energy equation including heat generated by the electrochemical reactions in the fuel cell. The present numerical model includes the gas diffusion layers (GDL) and serpentine channels for both anode and cathode gas flows, as well as cooling channels. To accurately predict the water transport across the membrane, the distribution of water content in the membrane is calculated by solving a nonlinear differential equation with a nonlinear coefficient, i.e., the water diffusivity which is a function of water content as well as temperature. Main emphasis is placed on the heat transfer between the solid bipolar plate and coolant flow. The present results show that local current density is affected by cooling channels due to the change of the oxygen concentration and the membrane conductivity as well as the water content. It is also found that the relative humidity is influenced by the generated water and the gas temperature and thus it affects the distribution of fuel concentration and the conductivity of the membrane, ultimately fuel cell performance. Unit-cell experiments are also carried out to validate the numerical models. The performance curves between the models and experiments show reasonable results.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.1
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• pp.45-53
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• 2013

Fuel cell power system is one of the most promising energy source for the alternative energy because it has unique advantages such as high energy density, no power drop during operation, and feasible to make compact size. However, due to very low response time, fuel cell is difficult to correspond to drastic load changes and start-up operation. For solving these problem, fuel cell power system must include energy storage device such as Li-Poly battery or super capacitor. Therefore, bi-directional DC-DC converter must be required for this storage device and fuel cell-PCS control. This paper presents a design and modeling of the bi-directional DC/DC converter. Firstly, we present modeling the boost and buck mode of the bi-directional converter through both PWM switch model and state space averaging technique. Secondly, in order to minimize output ripple and transient response overshoot, we have two identical DC-DC converters interleaved and adopt two-loop voltage-current controller. The proposed bi-directional DC-DC converter's modeling method and control design have been verified with computer simulation and experimentation.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.9
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• pp.100-108
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• 2003

This paper proposes a flywheel hybrid vehicle to solve the energy crisis problem by the exhaustion of a fossil fuel and air pollution for the conservation of environment. The proposed flywheel hybrid vehicle is composed of an accumulator and a flywheel as the energy generation and storage component and three variable displacement hydraulic pump/motors as the energy transfer devices. Flywheel has the characteristics of high energy density and easy energy absorption and consumption. The effectiveness of the energy-saving of the proposed flywheel hybrid vehicle is verified by simulation using Matlab/simulink. First of ail, analytical modeling for the flywheel hybrid vehicle is presented and simulations are performed based on the experimental efficiency data of a variable displacement pump/motor. The results of the simulation show that the effect of energy savings is realized by the proposed hybrid vehicle in 3 different city driving patterns.

• Carbon letters
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• v.15 no.4
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• pp.262-267
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• 2014

Pyrolized fuel oil (PFO) was reformed by novel electron beam (E-beam) radiation, and the elemental composition, chemical bonds, average molecular weight, solubility, softening point, yields, and density of the modified patches were characterized. These properties of modified pitch were dependent on the reforming method (heat or E-beam radiation treatment) and absorbed dose. Aromaticity ($F_a$), average molecular weight, solubility, softening point, and density increased in proportion to the absorbed dose of E-beam radiation, with the exception of the highest absorbed dose, due to modification by free radical polymerization and the powerful energy intensity of E-beam treatment. The H/C ratio and yield exhibited the opposite trend for the same reason. These results indicate that novel E-beam radiation reforming is suitable for the preparation of aromatic pitch with a high ${\beta}$-resin content.

• Proceedings of the KIPE Conference
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• 2007.11a
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• pp.151-153
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• 2007

Recently study on components for a electric golf car and a utility car driven by a electric motor has been performed actively, and the study on a drive motor, a inverter and a battery focuses on a small, light weight and high power density source to improve fuel efficiency using limited electric energy. Especially, since a utility car such as a golf car performance depends on initial acceleration and maximum speed capability, a drive system requires high power and large and wide operation area, This study therefore investigates on the interior permanent magnet synchronous motor with high power density and wide operation, and is verified with the test result after design and characteristic analysis is performed.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1025-1026
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• 2007

Recently study on components for a electric golf car and a utility car driven by a electric motor has been performed actively, and the study on a drive motor, a inverter and a battery focuses on a small, light weight and high power density source to improve fuel efficiency using limited electric energy. Especially, since a utility car such as a golf car performance depends on initial acceleration and maximum speed capability, a drive system requires high power and large and wide operation area, This study therefore investigates on the interior permanent magnet synchronous motor with high power density and wide operation, and is verified with the test result after design and characteristic analysis is performed